Need help with adder and BCD logic

Thread Starter

AldrinDB

Joined Nov 15, 2023
1
Hi, Is there somebody who could help me with my project regarding an adder which has 2 digits (0-99) each addend with 2-digit, 7-segment display and a sum of 3-digit (0-198) with 3-digit, 7-segment display? Your help would be much appreciated.

Moderator edit: New thread created from old thread.
 

AnalogKid

Joined Aug 1, 2013
10,944
You are replying to a thread that died over 13 years ago. Better to start your own thread, and reference this one with a link.

Also, your question needs a lot more detail. Do you want to add the BCD signals, or the 7-segment signals going to the displays?

Is this a school assignment?

ak
 

Papabravo

Joined Feb 24, 2006
20,996
If this was 1974 you would have more available options, but there is not much call for those kinds of chips anymore because they have been replaced by more efficient solutions in terms of cost, board space and development time. We do things differently now and you're just going to have to adjust to the new realities.

The 74185 mentioned in the other thread was actually a ROM (Read Only Memory) programmed with the appropriate look-up-table. IMHO, a microcontroller or an FPGA is the only practical method to succeed with this project in a reasonable time frame with a reasonable budget. Another upside is that it will be the first step in being able to tackle more challenging and useful projects.

ETA: You can implement a two-digit BCD adder with four 74HC283 4-bit binary adders, one quad 2-input AND gate package and one three input NOR gate package and one 74HC04 hex inverter package for a total of seven packages just for the adder. BCD to 7-segment decoders and dip switch entry will increase the count to a dozen or so packages. That going to be a job of work to fabricate and debug.
 
Last edited:

dl324

Joined Mar 30, 2015
16,679
Welcome to AAC!
Is there somebody who could help me with my project regarding an adder which has 2 digits (0-99) each addend with 2-digit, 7-segment display and a sum of 3-digit (0-198) with 3-digit, 7-segment display?
It would be helpful if you posted the entire text for the problem so we can see what constraints you have. Are you simulating this? Or actually breadboarding?
 

Papabravo

Joined Feb 24, 2006
20,996
  1. Get the datasheet for the 74HC283. It is a 4-bit binary adder.
  2. Get the datasheet for the 74HC08. It is a quad 2-input AND gate.
  3. Get the datasheet for the 74HC32. It is a quad 2-input OR gate.
  4. Make a truth table for BCD addition derived for the results of binary addition.
Hint #1: If the sum of two 4-bit binary quantities is between 0 and 9, it is the same as the BCD result.
Hint #2: If the sum of two 4-bit quantities is between 10 and 19, there is a simple correction to transform the binary result into the correct BCD result.
 
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